Modern wireless communication devices, including mobile telephones and other portable radio communication devices, offer an expanded set of features that are increasingly dependent on bandwidth and require complex circuitry for performing the multitude of functions that enable those features. One such feature is the flexibility to operate under multiple communications standards and/or across multiple bands of operation to enable interoperability between existing and emerging radio access technologies (RATs) and/or to accommodate international business and recreational travelers. Another feature is the ability to provide high speed, high data rate wireless communications in order to satisfy the growing demand for connectivity in an increasingly mobile world.
To provide at least these features, mobile communications devices now have an increasing number of antennas, covering multiple frequency bands and both cellular RATs and non-cellular RATs. The cellular RATs may include, for example, GSM (Global System for Mobile Communications), EDGE (Enhanced Data Rates for GSM Evolution), UMTS (Universal Mobile Telecommunications System), and LTE (Long Term Evolution). Note that each of these RATs can be considered evolutions of the same platform and are colloquially referred to as 2G, 2.5G, 3G, and 4G technologies, respectively. CDMA (Code Division Multiple Access) is another cellular RAT and can be considered a competing 3G technology that blends into LTE's 4G technology. The non-cellular RATs may include, for example, Bluetooth®, Near Field Communication (NFC), Wireless Local Area Network (WLAN, a.k.a. WiFi), Wireless Metropolitan Area Networks (WMAN, a.k.a. WiMax), Radio Frequency Identification (RFID), Global Positioning System (GPS), etc. The increasing number of antennas has created an increasing number of antenna design challenges related to isolation, efficiency, bandwidth, impedance matching, insertion loss, and other related factors.
Further, because each RAT may support one or more frequency bands, and each frequency band of a given RAT may be assigned to specific regions of the world and/or specific wireless communication carriers, global mobile device manufacturers often create multiple carrier, region, and/or RAT-specific versions or variants of their mobile devices in order to have a presence in various markets around the world. Each of these variants may include antennas and accompanying wireless communication circuitry (e.g., switches, power amplifiers, filters, duplexers, signal paths, transceivers, etc.) that are specifically tuned or optimized for the particular RAT(s) and/or frequency bands supported by the variant, thus increasing costs and manufacturing complexity. For example, some mobile device manufacturers may design a different antenna layout for each wireless communication carrier based on the specific RATs and/or frequency bands associated with the carrier.
Competing with the increasing demands on the radio portion of the mobile device is the constant push to minimize the size, weight, power consumption, and cost of mobile devices. A couple ways to minimize these characteristics include reducing the number of components and/or connections within the device and performing multiple functions using the same components. To that extent, some commercially-available mobile devices include one or more multi-band antennas that are capable of selectively operating in one of a plurality of frequency bands at a time. This arrangement reduces the total required antenna volume when compared against the alternative of a greater quantity of antennas, each having fixed and narrower bandwidth. However, multi-band antennas also add to the design complexity of the radio portion. For example, each multi-band antenna typically requires antenna matching circuitry, or an antenna switch module, as an interface between the antenna and the wireless communication circuitry in order to provide appropriate impedance matching over each frequency of operation. The more frequency bands covered by a mobile device, the more complicated the antenna matching circuitry. Thus, despite efforts to broaden the antenna coverage provided by mobile devices, most commercially-available mobile devices are still incapable of providing complete coverage for all RATs and/or frequency bands without significantly increasing the antenna volume, and complexity, of the device.
In view of the above antenna design challenges, most commercially-available mobile devices include radio portions that can only operate in, and/or are specifically optimized for, certain frequency bands, each of which is allocated to a specific wireless communication carrier. As a result, if users want to switch from one carrier to another, they may also need to switch their mobile devices if their existing devices are incompatible with the frequency bands covered by the new network. Many cost-conscious users may want to switch carriers fairly often in order to take advantage of lower pricing and attractive promotions, such as introductory service rates with terms of expiration. But the prospect of switching mobile devices can be a huge deterrent. For example, switching to a new device involves the cumbersome task of moving photos, contact information, emails, call and text messaging history, applications, and other data stored in the old device to the new device. Users may be reluctant to part from their existing devices for other reasons as well, including familiarity and/or the addition of personalized touches (e.g., customizing the rear housing, adding skins and other embellishments, etc.). Lastly, the cost of switching devices is usually passed on to the consumer in the form of higher service rates. Retaining an already-owned mobile device, while switching carriers can improve service plan options and costs.
In some cases, even if the radio portion of the mobile device is operable in the bands of the new carrier, the user's existing device may be “locked” to the existing carrier. As a result, the mobile device cannot be used with the new carrier's service (except when roaming). Carrier-locks are most common in mobile devices that are heavily subsidized by the carrier and the business model depends on the customer staying with the carrier for a minimum term to recoup the cost of the subsidy. In some cases, the mobile device is locked to a carrier-provided subscriber identity module (SIM) card, such that the device only works with SIM cards from the specific carrier. While a carrier-, or SIM-, locked device can be unlocked by, for example, entering a special code or numeric password, such processes are questionable in some regions (e.g., the United States) and may be too complicated for the average user.